Background: Patient safety is a priority in all health-care centers across the world. This study aimed to determine the frequency of events that threaten patient safety and the grade threating of events from the perspective of the health-care professionals in the intensive care units (ICUs). Materials and Methods: This cross-sectional study was conducted in 2016. The participants were 306 members of health-care professionals (physicians and nurses) with at least 1 year of work experience in ICUs of educational hospitals affiliated to Isfahan University of Medical Sciences. Data were collected using a three-section self-made questionnaire. Data analysis was done using descriptive statistics (frequency distribution and percentage) and version 16 of SPSS software. Results: A total of 306 questionnaires were completed out of 320 questionnaires handed out among participants. During the last month, 91.2% of the participants had reported at least a case of medication error, 75.6% had reported at least a case of ventilator-associated pneumonia, and 74.2% had reported at least a case of catheter-induced urinary infection in ICUs. Conclusion: The occurrence of events threatening the patient safety in ICUs warrants proper planning by administrators of health-care centers. Medication error was the most frequent and important event of threat to patient safety and falling was the least frequent event of threat to patient safety in ICUs. Considering the frequency and magnitude of medication error in ICUs, a well-adjusted preventive plan should be designed and implemented to improve the patient safety.